Stoker control



May 13, 1943- A. T. RANKIN STOKER CONTROL Filed June 24, 1939 5 Sheets-Sheet 1 May 1s, 1943. A T, RANK'IN 2,319,774

' STOKER CONTROL Filed June 24, 1939 5 Sheets-Sheet 2 rToP/v: r6

AL T. RANKBN STOKER CONTROL 35 G A mfalz N Oo o W 1l a0 Tf. T t E 6 V T .M O O N0, N a `fw jm .3% au. 3 o o A Mw@ Y @n u e w m A@ela MMM. m S m 1 .mw o mm@ mi z 4 4 n z me C .n 8 a z F. C (d 2 W 7 `\0 A 1v. 1711...- J S y n mx a May 18, 1943. A. r. RANKIN s'roKEn coNTRoL Filed June 24. 1959 5 Sheets-Sheet 5 POOH THEHIST'AT "HOT .sv-Aar maw/parar com 1 COLD Patented May 18, 1943 STOKER CONTROL Armand T. Rankin, Indianapolis, Ind., assignor,

` by direct and mesne assignments, of one-half to Sun-Fire Stoker Corporation, a corporation of Indiana, and one-fourth to William J. Bash,

Champaign, lll.

Application June 24, 1929, Serial No. 280,900 A '7 Claims. (c1. 23e-9) This invention relates to means for controlling the operation of a stoker for supplying fuel to a combustion zone in a furnace or the like, and

has for a primary object the provision of a structure that is exceedingly simple and at the same time highly eilicient in maintaining the rate of combustion within limits as predetermined. 'I'he invention is equally well adapted to natural draft as to forced draft conditions, the structure being particularly suitable in natural draft installations.

The invention provides means for positively opening and closing dampers in accordance with the demand for heat automatically under the control of thermostats in both the space to be heated and either in the stack or in the dome of the furnace as a high limit control. 'I'he entire control, not including thethermostats just indicated, may be assembled within a convenient receptacle which may be mounted at selected positions adjacent the furnace depending upon the particular location and availability ofspace.

'I'hese and many other objects and advantages of the invention will become apparent to those versed in the art in the following description of the invention as illustrated more or less diagrammatically in the accompanying drawings, in which Fig. lis a diagrammatic layout in side elevation of a heating system to which the invention Fig. 7. a detail in vertical Asection on the line 1-1 in Fig. 8;

Fig. 8, a detail in side elevation of a switch unit shown in Fig. 5;

,Fig. 9, a schematic wiring diagram to natural draft; and Fig. 10, a schematic wiring diagram for forced draft conditions.

applying Like characters of l,reference indicate like parts Athroughout the several views in the drawings.

Referring to Fig. 1, a conventional type furnace Il is shown as ,havinga conventional type stoker -Ii connected therewith and operated by an electric 4motor l2. The ash pit `damper Il (natural draft being employed in the present example) and a stack damper door Il are interconnected through a suitable cable I5 with the arm I8 extending from the control box l'l. A high` temperature limit thermostat unit i8 is employed either in the dome of the furnace or in the stack, herein shown as a unit I8 mounted in the stack I9. A room thermostat 20 is placed in a room or space to be heated by the furnace i0. The room thermostat 2n and the stack thermostat i8 and also the motor I2 are electrically interconnected to devices within the control box i1 as will hereinafter more fully be explained.

Current from a suitable source is carried through suitable conductors into the control box i1.

The control box I1 is-shown on an enlarged scale with the front cover removed in Figs. 2-4 to illustrate the units therein. Where it is desired to employ a low voltage current, particularly in connection with the room thermostat, a transformer 2| is mounted Within the box l'l to step ydown the current from the usual 110 volt source to 17 volts. A damper operating motor 22 of the usual and well known type (the details of which do not enter into the present invention) carries a final drive shaft 23 to extend therefrom horizontally outwardly through a wall of the box I1 to carry the lever i8 on its outer end externally of the box. .A synchronous motor 24 is mounted in the box i1 below the motor 22 and has a final drive shaft 28 extending forwardly therefrom to carry a pair of spaced apart cams 28 and 21, each adjustable for peripheral contour.

A post 28 extends forwardly from the rear wallv of the box I1 to carry a pair of rockers 28 and 30 thereon, each normally individually free to drop by gravity to carry cam followers 3l and 32 into the paths respectively of the cams 21 and 28. Each of thev rockers 29 and 30 carries a mercury tube switch 33 and 38 respectively. The

rocker 30 has an arm 3l extending beyond the post 28 to terminate in an eye through which a rod 38 passes, vertically and freely. 'Ihe rod 28 carries a stop 31 limiting travel through the eye of the arm 38 so that the arm 35 may be pushed downwardly by pushing the stop 31 thereagainst.

The upper end of the rod 38 is connected to a cam follower 38 which is slidingly iltted abouty thev periphery of a cam'll that is fixed onr the damper motor-shaft 2l. For every revolution of the damper motor shaft 2l, the stop l1 on Vthe rod 28 will push downwardly on the arm I8 and thenglift upwardly to permit the return of the 88 to its normal upperposition. L

Referring now to Fig. 9, a pair of wires 4B and 4I lead from any suitable source of current, for examplell volts A. C., to connect with the synchronous motor 24 through the wires 42, 49 44 and' 45 whereby the-motor 24 is in continuous operation as long as any current is available in the wires 49 and 4|. This means that the cams 26 and 21 are continuously rotating at a constant speed determined by the gear ratio selected between the armature of the synchronous motor and its i'lnal drive shaft 25.

' The stoker motor I2 is intermittently operated for low fire maintenance by the opening and directly with the motor I2, while from the wire 42 there leads a wire 61, and the wire 43 to the switch 34, from the other side of which is carried a wire 49 to the wire 5I! which connects with the other side of themotor I2. Thus the motor I2 operates when the cam 21 is turned to close the switch 34 and ceases to operate when the switch 34 is lifted from its closed position to its open position, that position being indicated in Fig. 9. This operation of the stoker motor will continue independently of any demand forheat or lack of demand for heat in the space to be heated. For increasing the rate of combustion by supplying additional fuel, the second switch 33 is brought into operation by its operating cam 25 in between operations of the switch St, the cam 26 being turned on its shaft 25 to that required position. The switch 33 is in parallel connection with the switch 35 through the wires 5I and 52. switch 33 is the switch that controls the feeding of additional fuel to the combustion zone as the callfor additional heat is made by the room thermostat.

Where the transformer 2l is employed, its primary is connected between the wires 40 and Sl .by the respective wires 53 and 54. The secondary winding of the transformerv 2i has a wire 55 carried' therefrom directly to the damper motor 22. The other side of the secondary winding has a wire t leading therefrom to connect with a brush 51 to be in thepath of a segment 58 of a commutator fixed to the shaft 23`of the motor 22. In the present form, this brush 61 is in continuous contact for 360 degrees of travel of the cen-4 tral circular segment 58 of the commutator. A -second brush 59 is mounted to have an end spaced below the brush 51 to be in the path only oi! the segment Gt of the commutator. A third brush tl of the same segment 6B. A fourth brush $2 is mounted above the brush 3l to be in a third path in which the two curved major segments 93 and 84 travel. As indicated, these two segments 83 and'84 are a trifle less than 180 degrees in length and have adjacent ends at the top in the position shown, united through the segment lill with the central segment 58 while the other ends of the segments 63 and B4 are spaced apart one from the other. Also it is to be noted that immediately below the segment 60 there is a central gap left between the ends of the segments 63 and Btl. s The damper motor 22 has been operated Vto bring the 4commutator to the position shown in Fig. 9 which is that position where the furnace dampers have been operated to an off" or hold flre condition, that is, the damper'IB has been closed and the damper I4 opened, Fig. l. Likewise the room thermostat element 20 has left the contact member 12 and traveled to some position is mounted above the brush` 51 to be in the path either intermediate that contact 12 or entirely,

Athe cold contact member 10.

Now assuming that the room thermostat again calls for heat, this condition will be indicatedwhen the bimetal member B1 has traveled back against the contact member 12. When this happens, a circuit is closed from the contact closing of the switch 34 as determined by the cam 21. From the wire 44 is a wire 48 connecting -member 12 vthrough the wire 65, brush 69, comcommutator starts revolving in the direction ofA the air indicated for substantially 180 degrees of travel of that commutator and, of course, of the shaft 29 and the cam 38 thereon. This supply of current is obtained by reason of the fact that by the time the segment 69 leaves the brush E9, the segment t3 has come into contact with the brush t2 so that current from the winding 2t is then carried across the commutator segments 5t, t@

and 89 through the brush 62 and the wire l5 to the motor 2t, the return wire being the same wir@ te. The circuit is interrupted when the commutator segments reach the positions 180 degrees from those shown in Fig. 9.

Now should `for some reason the furnace become overheated before the demand is satisfied in the room in which the thermostat 2t is posi: tioned, andthe stack thermostat i8 has its bimetal member 99 shift over to the contact member 19, the circuit still remaining closed in the thermostat 20 between the. elements 61 and T12, a circuit will be closed through the members as follows: contact member 16, wire 1t, brush 6i, commutator segment @Il then being under that brush, commutator segment 58, brush 5l, wire 5B, winding 2l, wire 55, motor 22, wire 15, wire 1I, and the thermostat bimetal member 69. The closing of that circuit will, of course, set the damper motor 22 into operation to shift the cam '39 around to the closed damper positions so as to check the fire even though the room ther= mostat be calling for additional heat. Then when the furnace has cooled, 'the stack temperature will permit the bimetal member B9 to leave the lcontact 1B and again go against the contact member 79 whereupon the first indicated circuit is completed through the room thermostat bi= metal B1 then being against the contact member i2 so as to cause the damper motor 22 to operate again and restore the switch 33 to the increasing fire condition.

Then, in the normaloperatlon, the room thermostat bimetal B1, when the demand for heat has been met, shifts over against the contact 4 member 88, thereby closing a circuit through thc circuit. Closing of that circuit sets the damper motor 22 into -operation to bring it around back to the position as indicated in Fig. 9. 'Ihat is the position wherein the dampers are closed and only the hold nre switch 34 is operating, it being understood, of course, that the closed damper condition referred to is that condition wherein the ash pit damper I3 is closed and the stack damper I4 is open.

As above indicated, the commutator segments are so arranged in respectito the various brushes in their paths that once any circuit is closed by the thermostat elements 61 and 69, the commutator will revolve through approximately 180 degrees and then come to a stop and be left in a position wherein the other control circuits may again be closed through the commutator for additional operations.

Preferably the stack thermostat Il is madefto have the thermostat member 69 operate so that it is in either of the two extreme positions, either against the member 13 or against the member 16,

, without stopping therebetween. The mechanical details of such thermostat do not enter into the invention per se, particularly since that unit may be purchased complete at the present time.

Referring now to that modied form of the control unit as shown in Figs. -8, instead of employing the two mercury switches 33 and 34, contact switches may be employed to give the same results. In this case, instead of mounting the cams 26 and 21 on the sameshaft 25, the cam 26 alone is mounted on the shaft 25 of the motor 24 and the cam 21 is mounted on a separate shaft 16 driven by the motor 24 preferably at the same speed as that of the shaft 25 although this may be varied inaccordance with the predetermined requirements for fuel feeding for low fire conditions. To insure positive making and breaking of the circuits with the contact form of switch, I provide an additional cam behind each of the cams 26 and 21, such as is illustrated in Fig. 8 wherein a cam 19 is mountedimmediately behind the cam 26 to turn therewith in operation. A spring contact member 66 has one end curved around to bear against this cam 19 while a second spring contact member 3l has an outer end curved over into the path of the cam 26 to be operated thereby. These contact members 36 and 6I take the place of the terminals within the switch 33. In order to subject the circuit through these contact members 36 and 6i to control through operation of the damper motor 22, instead of employing the push rod 36, I place a spring switch 32 in the path of the cam 39 that is carried on the motor shaft 23 and adjust the cam 33 on that shaft so that when theshaft 23 is turned to that positionA wherein the draft is cut ci! through the furnace, this switch 62 by means of a plunger 63 bearing against ,the cam 33, Fig. 6, is pushed to an open position. The detailed construction of the switch 62 is well known to those versed in the art, since the switch is of that type normally employed to operate in conjunction with doors and the like so as to close when the door opens and open when the door shuts.

Referring to Fig. 10, a wiring diagram is illustrated, employing contact switch members 36, M,

and I6, I3 in place of mercury switches, and the diagram illustratesA a control system for forced draft conditions wherein the stack damper must be closed when 'fuel is fed to the furnace and air is forced in. In this form, the cam 39 directly operates the stoker control switch 32 to close a high voltage circuit volts in present example) to the stoker motor I2 in this case operating a Iblower as well as the fuel feeding means in the customary manner. The switch 32 is normally biased to a closed position and is opened by the cam 39 pushing on the,switch plunger 63. The cam 26 operates to make and break contact between the switch members 60, 3l which are normally in open positions, and the cam 21 operates to make and break contact between the switch members 66, 83 which are normally in lclosed positions, in the form herein shown. Cams 26 and 21 are arranged to hold the members 80, 6I in the open condition when the members 66, 93 are in the closed condition, and vice versa during rotation of the cam shaft 25.

Referring to Fig. 10, the various elements, such as the stack thermostat I6, room thermostat 20, damper motor 22, and stoker motor I2, are all shown in those positions wherein the entire control system is inoperative due to the fact that the stack thermostat bimetal element 69 has become sufficiently heated at the furnace to shift to the high heat limit side of the thermostat and thereby cut off all control circuits insofar as they may affect the operation of the Stoker motor. In this condition, tracing the primary circuits, omitting names of the wires or the elements and simply referring to them by the identifying numerals, starting at the stack thermostat high linut contact 10, the circuit runs through 1I, 13, and 6I, a, brush whose end is in .l open circuit in reference to the segment 60 of the damper motor driven commutator. Thus it is to Ibe seen that the operation of the stack thermostat to its high limit condition serves as an absolute'control on the entire system, preventing operation thereof.

Now assuming that the stack thermostat element 69 drops back against the cold contact 16 to restore the control system to an operative condition following the cooling down of the furnace, and also assuming that the room lthermo-- stat bimetal element 61 is against its contact 12, which is the condition when the room thermostat vis calling for no heat, then the following situations may exist. Beginning with the stack thermostat contact 16, a circuit is had through 95, 66-93, 9|, 65, 59, 60, 58, 51, 56, 2|, 55, 22, 15, 66,69, to 16. This completes a circuit including the damper motor 22 and the secondary transformer winding 2I which causes the motor 22 to operate to revolve degrees the commutator segment 60, placing it under the brush 6I and leaving the brush 59A in open circuit. Also the cam 39 has revolved to permit the switch 82 to go to a closed position and thereby close the primary circuit of the stoker motor. Furthermore, the arm I6 has revolved 180 degrees to bring the draft dampers to those positions to permit full draft through the furnace-this condition being necessary at all times when the stoker motor is in operation Now since the synchronous motor 24 is in continuous operation irrespective of the stoker motor operation and irrespective of the positions of the two'thermostat elements 61 and 69, the cams 26 and 21, driven by the motor 24,' will be continuously turning, alternately` opening and or length of the surfaces oi' the cams 26 and 21. For example, these cams may be driven at a speed that will cause the switches in each instance to operate once every ten or fteen minutes, this period of time being merely set out as an eX- 'l ample without any limitation as to the actual practice since this period is quite variable in accordance with the actual firing conditions encountered.

Keeping in mind that the commutator seg-A ment t@ has been carried around under the brush t and that the stoker motor i2 is operating, an intermittent control of that stoker motor and of the dempers accordingly is set up through operations of the cams 2B and t1 all during this period when the room thermostat is calling for no heat. In other words these cams serve to change the control circuits whereby the stoker motor is intermittently operated just sumciently to keepthe fire burning properly without giving off an excessive amount of heat or such heat that would materially change the temperatures of the space to be heated. That is to say, a hold hre condition is set up even though there be no demand for heat.

Checking again in the diagram of Fig. ll0, under this condition, the switch members SS and @t are opened after an interval of normal closure as controlled by the cam 2l and, of course,

the switch members t@ and ti then close. The

circuit is then from the stack thermostat contact it through e5, s2, Sc-'i, Qt', ti, i2, llt, ti, tu (segment tu then being under ti), 58, El, 5S, 2i, 55, 22, l5, t8, t9 to it. The creation ofcthis circuit closure causes the motor 22 :to operate and return the commutator segment t@ back to the position in Fig. 10 and, furthermore, operates the dempers to the shut oif draft condition and also actuates the switch @i to an open position to stop the stoker motorI i2. n

Now when the condition exists that the space to be heated requires heat, the room thermostat element 6i' shifts into contact with the contact member dt, Fig. 10. 'It is assumed that the stack thermostat element t9 remains in contact with its cold contact lt. Under this condition, there will be no intermittent operation of the dempers and stoker motor but the stoker motor will be set into operation to permit it to continue until the heat demand is satisfied and the room thermostat velement .el switches back over and against the other contact member 172.

With the room thermostat in that conditionA calling for heat, the control circuit is traced as follows, beginning at the stack thermostat contact member it and continuing through 35,

t9, to it. The closure of this circuit causes the damper motor 22 to operate, shifting 180 degrees the commutator segment @t to position it under the brush 6i; Arevolvingr the arm it to shift the dempers to a full open draft condition: and

permitting the switch 82 to close and permit the c stoker motor i2 tooperate. This circuit has been traced in the assumption that the switch. members t@ and Si were initially'open andthe switch members B8 and tt were initially closed. 'If the reverse conditiony existed, the following circuit would be had gto setthe stoker motor i2 in operation: it, t5, 92,' tu, di, ed, 575,166, 9d, @5. 5S, t6,

'58, N, 5B, 2l, 5b, 22, TIB, S8, 38, to '11%. Continuous operation 'of the cams 26 and 21 thereafter do not cause any changes in either of these cir cuits such as would again cause the damper motor 22 to operate to stop the stoker motor it aslong ment G9 shifts to that position shown in Fig. 10 to be in contact with its contact member 16. In

so doing, the following circuitis established:` 'l0 lil, 13, di, Si) (segment 60 will come under brush Si during the intermittent operation of the stoker motor asabove described), 58, l, `'56, 2i, 55, 22, i6, 6B, t9. This circuit brings the stoker motor 22 into operation to cause the commutator segment 6@ to revolve around to that position indicated in Fig. as well as to permit the switch d2 to go into its off position to stop the stoker motor. Should the room thermostat element 8l be against the contact member t6, the same condition would prevail as just described since the circuit would be open in any event between the element t? and the contact member it.

The commutator, above described as being mounted on and driven by the shaft 23, is so arranged as has been indicated: to control the circuits whereby the shaftZS rlevolves 180 degrees and then stops at each energization of the motor 222 so that the segment 60 is always in one of two positions, namely, the position shown in Fig. l0 or in a position under the brush Si. This commutator arrangement is not, per se, a part of this invention but is found in a commercial form of a damper motor unit obtainable upon the market.

In referring to :the stoker, I mean to include both solid and liquid fuel feeding devices. Closing the draft after oil firing prevents much heat loss, otherwise occurring by heat escaping up the stack.

While I have herein shown and described my invention in the best form as known to me, it is obvious that structural changes may be employed without departing from the spirit of the invention and I, therefore, do not desire to be limited to that precise form beyond the limitations as may be imposed by the following claims.

t I claim:

l. For controlling a motor driven stoker applied to a heater having a draft control damper, a control system comprising in combination, a. high temperature limit thermostat switch at the heater; a room temperature responsive thermostat switch: a stoker motor control switch; a damper operating motor; a damper motor control switch operated by the damper motor; means t0 driven by the damper motor to actuate ysaid stoker motor switch; an intermittent switch: a second intermittent switch; means continuously operating both of the intermittent switches between on and oilpositions at a predetermined o5 rate of speed; anda circuit including a source of electrical energy, said damper motor .control switch, -said damper motor, said intermittent switches, said room thermostat switch' in a room noheatdemand condition, and said high temperature limit switch, said circuit being closable by one of said intermittent switches through said damper motor control switch only upon said high temperature limit switch being in its cold positin, said damper-motor control switch being f'I-iormed to close the circuit through the damper motor to operate that motor to the open draft position and then stop that motor upon each closure of said one intermittent switch, and upon closing of the other intermittent switch, to again close the circuit through said damper motor to cause that motor to operate to the closed draft position, said stoker motor switch being closed and opened by the damper motor in accordance with open draft and closed draft damper positions.

2. For controlling a motor driven stoker applied to a heater. having a draft control damper, a control system comprising in combination, a high temperature limit thermostat switch at the heater; a room temperature responsive thermostat switch; a stoker motor control switchya damper operating motor; a damper motor control switch operated fby the damper motor; means driven by the damper motor .to actuate said Stoker motor switch; an intermittent switch; a second intermittent switch; means continuously operlating both of the intermittent switches beween on and off positions at a predetermined rate of speed; and a circuit including a source of electrical energy, said damper motor control switch, said damper motor, said intermittent switches, said room thermostat switch in a room no-heatdemand condition, and said high temperature limit switch, said circuit being closable by one of said intermittent switches through said damper motor control switch only upon said high temperature limit switch being in its cold position,

'said damper motor control switch being formed to close the circuit through the damper motor to operate that motor to the open draft position and then stop that motor upon each closure of said one intermittent switch, and upon closing of the other intermittent switch, to again close the circuit through said damper motor to cause that motor to operate to the closed draft position, said stoker motor switch being closed and opened by the damper motor in accordance with open draft and closed draft damper positions; and another circuit including said room thermostat switch in a room heat demand position, said damper motor switch, and one of said intermittent switches, said other circuit being arranged to have its said included intermittent switch close the circuit to energize the damper motor to have it operate to its open draft position and stop and vrenziain in that position irrespective of subsequent operations of both intermittent switches until said last circuit is interrupted by said room thermostat switch shifting from said room heat demand position to a no-heat-demand positio 3. For controlling a motor driven stoker aoplied to a heater having a draft control damper, a control system comprising in combination, a high temperature limit thermostat switch at the heater; a room temperature responsive thermostat switch; a stoker motor control switch: a damper operating motor; a damper motor control switch operated by the damper motor; means driven by the damper motor to actuate said stoker motor switch; an intermittent switch; a second internimittent switch; means continuously operating both of the intermittent switches between on and of! positions at a predetermined rate of speed; and a circuit including a source of electrical energy, said Ydamper motor control switch, said damper motor, said intermittent switches, said room thermostat switch in a room no-heatdemand condition, and said high temperature limit switch, said circuit being closable by one of said intermittent switches through said damper motor control switch only upon said high temperature limit switch being in its cold position, said damper motor control switch being formed to close the circuit through the damper motor to operate that motor to the open draft position and then stop that motor upon each closure of said one intermittent switch, and upon closing of the other intermittent switch, to again close the circuit through said damper motor to cause that motor to operate to the closed draft position, said stoker motor switch being closed and opened by the damper motor in accordance with open draft and closed draft damper positions; said intermittent switches alternating one with the other between said on and oif positions.

4. For controlling a motor driven stoker applied to a heater having a draft control damper, a control system comprising in combination, a high temperature limit thermostat switch at the heater; a room temperature responsive thermostat switch; a stoker motor control switch; a damper operating motor; a damper motor control switch operated by the damper motor; means driven by thev damper motor to actuate said stoker motor switch; an intermittent switch; a second intermittent switch; means continuously operating both of the intermittent switches between on and oft positions at a predetermined rate of speed; and a circuit including a source of electrical energy, said damper motor control switch, said damper motor, said intermittent switches, said room thermostatl switch in a room no-heat-demand condition; and said high temperature limit first switch, a second circuit including said electrical energy source, said damper motor, said high temperature limit switch, said damper motor controlswitch, and either of two parallel branches, one of said branches including said room thermostat switch, in a room heat demand 'condition and one of said intermittent switches, the other said branch including the other said intermittentv switch, said circuit being closable by one of said intermittent switches throughsaid damper motor control switch only upon said high temperature limit switch being in its cold position,

said damper motor control switch being formed to close the circuit through the damper motor to operate that motor to the open draft position and then stop that motor upon each closure of said one intermittent switch, and upon closing of the other intermittent switch, to again close the circuit through said damper motor to cause that motor to operate to the closed draft position, said stoker motor switch being closed and opened by the damper motor in accordance with open draft and closed draft damper positions; said intermittent switches alternating one with the other between said on and cif positions, said second circuit being closable through either one of said intermittent switches to operate the damper motor and the stoker motor to respective open draft and operating conditions, whereby said conditions will continue until the room thermostat switch restores said intermittent switches to intermittent control by moving to the no heat demand position.

5. For a system having a heater, a heater draft damper, space to be heated, and a motor driven stoker for supplying fuel to said heater, a stoker control comprising a damper operating motor; a heater temperature responsive thermostat having cold" and hot" circuit closing positions; a space temperature responsive theremostat having cold and hot circuit closing positions; a damper motor switch; time controlled hold-fire means periodically causing energization through said space thermostat in its "hot position and the heater thermostat in its "cold position and said damper motor switch of the damper motor to open draft position and subsequently to closed draft position; and means actuated by the damper motor causing energization and deenergization of the stoker motor in accordance with said open and closed draft positions.

6. For a system havingA aheater, a heater draft damper, space to be heated, and a motor driven stoker for supplying fuelto said heater, a stoker control comprising a damper operating motor; a heater temperature responsive thermostat having coldf and hot circuit closing positions; a space temperature resmnsive thermostat having cold and hot circuit closing positions; a damper motor switch; time controlled hold-lire means periodically causing energlzation through said space thermostat in its hot position and the heater thermostat in its cold position and said damper motor switch of the damper motor to open draft position and subsequently to closed draft position; and means actuated by the damper motor causing energization and deenergization oi the stoker motor in accordance with said open and closed draft positions; and means maintaining said damper motor in its open draft position lrrespective of said time controlled means during call for heat in said space as indicated by said space thermostat; said time controlled means tali` ing over control of the damper motor upon said space heat call being satised.

asians 7. For a swstem having a heater, a. heater draft damper, space to be heated, and a motor driven stoker for supplying fuel to said heater, a stoker control comprising a damper operating motor; a

position and subsequently to closed draft posi, ,l5

tion; and means actuated 'by the damper motor causing energization and deenergization of the Stoker motor in accordance with said open and closed draft positions; and means maintaining saiddamper motor in its open draft position irrespective of said time controlled means during call for heat in said space as indicated by said space thermostat; said time controlled means taking over control of the damper motor upon said space heat call being satisded; and said heater thermostat removing both said space thermostat and said time controlled means from control of said damper motor upon said heater reaching a y predetermined high temperature limit.

ARMAND T. RANKIN. 

